题意
思路
- 没有用匈牙利算法，而是试了试要带去的两个最大流模板。。
- 就是加一个源点，一个汇点，源到二分图集合1的点加一个流量为1的边，集合1到集合2的边设置为流量1，集合2的点到汇点加入流量1的边
实现
#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
#include <cstdio>
#include <vector>
using namespace std;
const int MAXN = 2000;
const int maxn = 2000;
const int MAXM = 20005;
const int INF = 0x3f3f3f3f;
struct Edge
{
int to,next,cap,flow;
}edge[MAXM];
int tol;
int head[MAXN];
int gap[MAXN],dep[MAXN],pre[MAXN],cur[MAXN];
void init()
{
tol = 0;
memset(head,-1,sizeof(head));
}
void addedge(int u,int v,int w,int rw = 0)
{
edge[tol].to = v;
edge[tol].cap = w;
edge[tol].next = head[u];
edge[tol].flow = 0;
head[u] = tol++;
edge[tol].to = u;
edge[tol].cap = rw;
edge[tol].next = head[v];
edge[tol].flow = 0;
head[v] = tol++;
}
int sap(int start,int end,int N)
{
memset(gap,0,sizeof(gap));
memset(dep,0,sizeof(dep));
memcpy(cur,head,sizeof(head));
int u = start;
pre[u] = -1;
gap[0] = N;
int ans = 0;
while(dep[start] < N)
{
if(u == end)
{
int Min = INF;
for(int i = pre[u]; i != -1;i = pre[edge[i^1].to])
if(Min > edge[i].cap - edge[i].flow)
Min = edge[i].cap - edge[i].flow;
for(int i = pre[u];i != -1;i = pre[edge[i^1].to])
{
edge[i].flow += Min;
edge[i^1].flow -= Min;
}
u = start;
ans += Min;
continue;
}
bool flag = false;
int v;
for(int i = cur[u];i != -1;i = edge[i].next)
{
v = edge[i].to;
if(edge[i].cap - edge[i].flow && dep[v] + 1 == dep[u])
{
flag = true;
cur[u] = pre[v] = i;
break;
}
}
if(flag)
{
u = v;
continue;
}
int Min = N;
for(int i = head[u];i != -1;i = edge[i].next)
if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)
{
Min = dep[edge[i].to];
cur[u] = i;
}
gap[dep[u]]--;
if(!gap[dep[u]])return ans;
dep[u] = Min+1;
gap[dep[u]]++;
if(u != start)u = edge[pre[u]^1].to;
}
return ans;
}
int vis[maxn];
vector<int> g[maxn];
#define pb push_back
void dfs(int u){
for (int e=0;e<g[u].size();e++){
int v = g[u][e];
if (vis[v] == -1){
vis[v] = (vis[u] ^ 1);
dfs(v);
}
}
}
int main(){
int n,m;
cin>>n>>m;
int u,v;
for (int i=0;i<m;i++){
scanf("%d%d",&u,&v);
g[u].pb(v);
g[v].pb(u);
}
memset(vis,-1,sizeof(vis));
for (int i=1;i<=n;i++){
if (vis[i] == -1){
vis[i] = 0;
dfs(i);
}
}
init();
for (int i=1;i<=n;i++){
if (vis[i] == 0){
addedge(0,i,1);
for (int e=0;e<g[i].size();e++){
v = g[i][e];
addedge(i,v,1);
}
}
else{
addedge(i,n+1,1);
}
}
cout << sap(0,n+1,n+2) << "\n";
return 0;
}
#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
#include <cstdio>
#include <vector>
using namespace std;
const int maxn = 2000;
const int inf = 0x3f3f3f3f;
struct EdmondsKarp{
int n,m;
int g[maxn][maxn];
int flow[maxn];
int path[maxn];
queue<int> q;
void init(int nn=0)
{
n = nn;
memset(g,0,sizeof(g));
memset(flow,0,sizeof(flow));
memset(path,-1,sizeof(path));
}
void addOne(int u,int v,int yuan)
{
g[u][v] += yuan;
m += 2;
}
int bfs(int s,int t)
{
int i;
memset(path,-1,sizeof(path));
flow[s] = inf;
path[s] = s;
q.push(s);
while(q.size()>0)
{
int tmp = q.front();
q.pop();
for(i=0;i<n;i++)
{
if(g[tmp][i]>0 && path[i]==-1)
{
flow[i] = min(g[tmp][i],flow[tmp]);
path[i] = tmp;
q.push(i);
if(i==t)
{
break;
}
}
}
if(path[t] != -1)
break;
}
while(q.size()>0)
q.pop();
if(path[t] == -1)
return 0;
else
return flow[t];
}
int go(int s,int t)
{
int ret = 0;
while(bfs(s,t))
{
int now = path[t];
int pre = t;
ret += flow[t];
while(pre != s)
{
g[now][pre] -= flow[t];
g[pre][now] += flow[t];
pre = now;
now = path[now];
}
}
return ret;
}
}edk;
int vis[maxn];
vector<int> g[maxn];
#define pb push_back
void dfs(int u){
for (int e=0;e<g[u].size();e++){
int v = g[u][e];
if (vis[v] == -1){
vis[v] = (vis[u] ^ 1);
}
}
}
int main(){
int n,m;
cin>>n>>m;
int u,v;
for (int i=0;i<m;i++){
scanf("%d%d",&u,&v);
g[u].pb(v);
g[v].pb(u);
}
memset(vis,-1,sizeof(vis));
for (int i=1;i<=n;i++){
if (vis[i] == -1){
vis[i] = 0;
dfs(i);
}
}
edk.init(n+2);
for (int i=1;i<=n;i++){
if (vis[i] == 0){
edk.addOne(0,i,1);
for (int e=0;e<g[i].size();e++){
v = g[i][e];
edk.addOne(i,v,1);
}
}
else{
edk.addOne(i,n+1,1);
}
}
cout << edk.go(0,n+1) << "\n";
return 0;
}
